Hydraulic power brake booster and open center control valve therefor

ABSTRACT

A hydraulic power brake booster powered by power steering gear pump pressure and utilizing an open-center valve so that fluid flows through the booster without pressure reduction when the booster is not activated. The valve assembly includes a radially floating valve seat which provides for self-centering, permits a valve separation operation to pass viscous cold hydraulic fluid or any elements which may tend to overly restrict the valve. It also includes a valve face design providing entrance and exit angles defining a venturi-type passage conducive to laminar flow with consequent reduction in valve noise, and has a hydraulic reaction mechanism which includes an arrangement for supported line pressure.

United States Patent Shellhause 5] Oct. 24, 1972 [54] HYDRAULIC POWERBRAKE BOOSTER AND OPEN CENTER CONTROL VALVE THEREFOR [72] Inventor:Ronald L. Shellhause, 519 Bennert Drive, Vandalia, Ohio 45377 [22]Filed: Sept. 29, 1970 [21] Appl. No.: 76,473

UNITED STATES PATENTS 3,353,451 11/1967 Garrison et al ..60/54.5 P

Primary Examiner-Edgar W. Geoghegan Assistant Examiner-A. M. ZupcicAttorney-W. E. Finken and D. D. McGraw [57] ABSTRACT A hydraulic powerbrake booster powered by power steering gear pump pressure and utilizingan opencenter valve so that fluid flows through the booster withoutpressure reduction when the booster is not activated. The valve assemblyincludes a radially floating valve seat which provides forself-centering, permits a valve separation operation to pass viscouscold hydraulic fluid or any elements which may tend to overly restrictthe valve. It also includes a valve face design providing entrance andexit angles defining a yentur i-type passage conducive to laminar flowwith consequent reduction in valve noise, and has a hydraulicreactionmechanism which includes an arrangement for supported linepressure.

I 1 Claim, 3 Drawing Figures 1 2,330,610 9/1943 Natter ..137/509FOREIGNPATENTS OR APPLICATIONS 606,200 10/1960 Canada ..60/S4.6'P

HYDRAULIC POWER BRAKE BOOSTER AND OPEN CENTER CONTROL VALVE THEREFOR Theinvention relates to a hydraulic power brake booster using anopen-center valve arrangement, and more particularly to one in which aconical valve seat and valve face cooperate and are constructed so as toprovide a self-centering action as well as a venturi-type passage whichimproves laminar flow through the valve. The input valve member isstopped against the booster body to establish an open position of thevalve member, and the valve seat is stopped against the power piston,which in turn is also stopped against the cylinder body so that thevalve opening is established by the cylinder body. This permits thepower piston to move under the pressure influence of cold viscous oilthrough the valve opening without pulling the input valve member withthepower piston. The resulting piston travel rapidly increases theeffective valve opening and permits viscous cold oil to pass through thevalve as the valve operates without causing the brakes to be applied tosuch an extent that they will drag. The piston travel required to openthe valve to the necessary extent is relatively slight. This arrangementalso minimizes the pedal travel necessary to actuate the unit bypermitting the initial or atrest valve opening to be set for warm oilconditions. I

The valve seat is mounted in the power piston so that it is radiallymovable when the valve member engages the seat to position the valveseat concentrically with the valve input member. This insures aconcentric annular valve opening which will also minimize valve noise aswell as provide consistent valve controlling action.

The valve assembly also has a hydraulic reaction piston reciprocablymovable in the power piston and in the valve seat and arranged topivotally seal relative to the piston and valv'e seat to accommodate theradial floating movement of the valve seat. A supported line pressurespring between the hydraulic reaction piston and the valve seat providesfor hold-off of reaction force during the initial apply phase of thebooster to obtain proper power unit feel. A reaction snubber and snubberpiston are provided at the point of contact between the reaction pistonand the valve input member to further .eliminate valve noise and toprovide a damping arrangement for the reaction piston.

IN THE DRAWINGS:

FIG. 1 is a schematic representation of a vehicle power steering andbraking system embodying the invention.

FIG. 2 is a cross section view of the hydraulic brake booster used inthe system of FIG. 1.

FIG. 3 is an enlarged view of the valve input member portion of theopen-center valve provided in the booster of FIG. 2.

The booster 24 is connected to actuate a master cylinder assembly 30which provides brake pressure to the front brake system 32 and the rearbrake system 34 of the vehicle'in which the hydraulic system isinstalled. The booster 24i's also shown as being provided with anelectro-hydraulic pump 36 which is actuated when necessary to providesufficient hydraulic fluid flow and pressure availability to operate thebooster 24 when insufficient hydraulic fluid flow and pressureavailability is provided through conduit 20. The pump 36 is arranged tobe actuated as necessary, and may, for example, be actuated by a flowswitch 38 provided in one of the conduits, such as conduit 28. Thebooster assembly 24 is schematically illustrated as being controlled bythe vehicle brake pedal 40.

The booster assembly 24 is illustrated in detail in FIG. 2. The housing42 is formed to provide a cylinder 44. The rear end 46 of the cylinderprovides for booster mounting by means of studs 48. Cylinder rear end 46is also formed to provide a rearwardly extending sleeve 50 which isprovided with a bore 52 extending through the sleeve and rear end 46 andaxially aligned with the cylinder 44. The forward end 54 of the housing42 has a cylinder cover which is centrally apertured at 56 so that thebooster output push rod 58 extends therethrough and is reciprocablymoved when the brake is operated. A suitable seal 60 is also mounted incover 54. The cylinder seal 62 is provided with a seal support plate 64fitting against the inner wall of the cover 54, and a seal expander 66on the cylinder side of the seal.

The brake pedal assembly acts through the push rod 68 to actuate thebooster. The forward end of push rod 68 is connected to input member 70which is slidably received in bore 52 of sleeve 50 and extends into thecylinder 44. The inner portion of bore 52 is provided with an O-ringseal 72 and a V-block seal 74 which effectively prevent leakage ofhydraulic fluid between input member 70 and bore 52. A suitable boot 76is also mounted over sleeve 50 and push rod 68 to prevent contamination.

The cylinder 44 is divided by a power piston 78 into an inlet or powerchamber 80 and an outlet or exhaust In the system shown in FIG. 1, thepower steering I pump 10 is provided with a hydraulic fluid reservoir 12connected to the input side of the pump by conduit 14. The pump outputconduit 16 is connected to the power steering gear 18, which'is of theopen-center type so that in the at-rest position hydraulic fluid ispumped freelythrough the gear. The conduit 20 connects the output sideof the power steering gear 18 with the inlet 22 of the hydraulic powerbrake booster 24. The booster outlet 26 is connected to the sump orinlet side of the power steering pump 10 by conduit 28, thus completingthe hydraulic fluid circuit.

chamber 82. Piston 78 is reciprocably movable in cylinder 44 duringbrake booster operation and is urged to the brake release position byspring 83. The piston includes a sealed skirt section 84 which fitscylinder 44, and has atits rearward end a positioning abutment sleeve86. This sleeve is of smaller diameter than the skirt section 84 and issuitably notched as at 88 to permit full fluid communication between allportions of the inlet chamber 80. Piston 78 is also provided withpassage means interconnecting the inlet chamber and the outlet chamber82, the passage means including a passage 90 extending through thepiston wall and a stepped recess 92 which mounts the valve and reactionmechanism. The valve mechanism controls the flow of hydraulic fluid fromthe inlet chamber 80 to the outlet chamber 82 through the passage means,thereby controlling the pressure differential across the power piston78. The larger rearward portion of recess 92 provides a mounting for thevalve seat 94. The forward end 96 of valve seat 94 abuts against ashoulder 98 formed as a part of stepped recess 92. A valve seat springretainer 100 tits in the outer end of recess 92 and engages the valveseat 94 so as to position the valve seat against axial movement relativeto the power piston 7 8.

The valve seat has a cylinder-like skirt section 102 which is thesection between recess shoulder 98 and retainer 100. The outer peripheryof skirt section 102 is of substantially less diameter than the portionof recess 92 in which it fits so as to provide for radial movement ofthe valve seat. Retainer 100 engages the valve seat and permits suchradial movement while tending to hold the valve seat in any radialposition to which the valve seat is moved through its spring-like actionurging the valve seat end 96 against shoulder 98. As illustrated in FIG.2 of the drawing, the retainer 100 includes radially extending fingerswhich circumferentially engage the inner surface of the piston abutmentsleeve 86 when the retainer is pressed into that sleeve, and axiallylock the retainer in place toward valve seat skirt section 102 so as toengage the rear surface thereof and hold the valve seat end 96 inabutting relation with shoulder 98. It thus axially retains the valveseat in position, and

piston 110 has a small diameter forward land 112 I received in cylindersection 106 and rearward larger diameter land 114 received in cylindersection 104. A portion of reaction piston 110 between the lands isstepped to provide a mounting for the reaction piston snubber 1 16.Snubber 116 is positioned in cylinder section 108 and cushions forwardmovement of the mac tion piston 110. A groove 118 in power piston 78fluid connects inlet chamber 80 with cylinder section 108 so that thereaction piston 110 and the cylinder section 108 cooperate to define areaction chamber 120. Reaction piston 110 is generally cup-shaped andits forward face 122 at land 112 is provided with axially extendingpassages 124 which fluid connect outlet chamber 82, through passage 90and the forward portion of recess 92, with the downstream side of thevalve seat 94. A snubber piston 126 is secured to the rear side ofreaction piston face 122 and extends rearwardly in a manner and for thepurposes described below. A supported line pressure spring 128 ispositioned within reaction piston 110 and valve seat 92 so as to urgethe reaction piston forwardly relative to the valve seat against theforce of pressure in reaction chamber 120.

Valve seat 94 includes a frusto-conical seat face 130 with the largerface opening extending rearwardly and the smaller face opening extendingforwardly. The seat face is aligned coaxially with the power piston 78,the

input member 70, the stepped recess 92, the reaction piston 110, thesnubber piston 126, and the output push rod 58. The seat face isconstructed so that it extends at an angle of degrees to the common axis131 of these elements.

' The input member 70 includes a valve 132 formed to provide afrusto-conical valve face 134 which is positioned to mate with andextend through valve seat face 130. For descriptive purposes the valveand valve seat faces will be referred to as being conical, it beingunderstood that this term encompasses a conical section formed by thefrustum of a right circular cone. At the rearward side of valve 132, theinput member is provided with a snap ring 136 and immediately behind thesnap ring is a valve return bumper 138. The bumper is formed of arubber-like material and prevents the snap ring from directly contactingthe housing rear end 46, thereby cushioning the valve return and furthereliminating valve operating noise. A valve return spring 140 seats onsnap ring 136 at one end and on valve seat retainer at the other end tourge the valve faces apart and, therefore, position the valve 132 inrelation to the cylinder end wall 46 when the booster is at rest. Theforward end of input member 70, forward of valve face 134, is providedwith an end section 142 located within the chamber formed by recessedreaction piston in which spring 128 is positioned. The end section isprovided with a cylinder-like recess 144 which is somewhat larger indiameter than snubber piston 126. The rear end of snubber piston 126extends slightly into recess 144. A rubber-like snubber 146 is receivedvat the bottom of recess 144 and is slightly spaced from the sphericalend of snubber piston 126 when the booster is at rest.

The valve face 134 of valve 132 is comprised of a face forward surface147 and a face after surface 148 which join at the circumferential lineof contact 150. The forward and after face surfaces are frusto-conical,with the forward surface 147 forming the angle a relative to the axis ofthe valve, this angle being nominally 31. The face after surface 148forms the angle b relative to the axis of the valve and is nominally 29.This arrangement, with angle 0 of seat face nominally at 30, provides aventuri-like valve opening. By providing the proper entrance and exitthroat angles relative to the metering point defined by the valvecircumferential line of contact 150, with the valve faces being smoothlyfinished, a satisfactorily low valve noise level is achieved. Therelative valve throat angles have been found to be critical in that theyshould differ no more than 5 percent in relation to the nominal angle ofthe valve seat face. Since it is desired that abrupt changes indirection of fluid flow through the valve should be minimized, it ispreferable to have the valve seat face nominal angle be at about 30.

When the system is at rest, with the power steering pump 10 beingdriven, hydraulic fluid is permitted to flow freely through the powersteering gear 18 and the booster 24 and return to the pump withoutrestriction. When the vehicle is steered leftwardly or rightwardly, thepower steering gear 18 operates to build up a back pressure in conduit16 and establish a pressure differential to provide power to thesteering gear, as is well known in the art. When the vehicle brake isactuated by depression of the brake pedal 40, the input member 70 movesforwardly, closing the space between valve seat face 130 and valve face134. Initial closure will result in contact of the valve 132 with thevalve seat face 130, causing the valve seat to move radially, if it wasslightly off center, to align the valve seat with the valve. Suchalignment may also occur when the brake pedal is depressed while thepower steering pump is not operating. Due to the minimal width of thereaction piston lands 112 and 114, slight radial movement of the valveseat 94 is accomplished without binding the reaction piston 110. Thelands have a pivotally sealing engagement with their respective cylindersurfaces which accommodates the valve seat radial movement.

Upon restricting the hydraulic fluidflow from the inlet chamber 80 tothe outlet charnberi82, hydraulic pressure isbuilt up in the inletchamber-.to'establish a pressure differential across the power piston78. The increased pressure in inlet chamber 80"also acts in reactionchamber 120 to urge reaction piston 1'10 rearwardly against the force ofspring 128'. This initial reaction force is not transmitted to the inputmember 70 since the other end of spring 128 is seated on the valve seat94. The pressure difierential also urges the power piston 78 forwardlyagainst the force of piston return spring 83, overcoming that spring andmoving push rod 58 forwardly to actuate the master cylinder 30. As thepressure differential increases, reaction piston 110 is moved rearwardlyuntil snubber piston 126 engages snubber 146. Since this normallyhappens quickly when the brakes are quickly applied, the movement ofsnubber piston 126 rearwardly into recess 144 displaces hydraulic fluidfrom that recess in a dashpot manner, providing a cushioning effect inthe initial transmittal of reaction force to the input member 70.Further rearward movement of reaction piston 110 causes the snubber 146to be compressed as it transmits additional reaction force to the inputmember as the pressure differential across the power piston 78increases. It can be seen that at any required pressure dif ferentialthe valve system will reach a poised position wherein the valve openingbetween faces 130 and 134 is just sufficient to maintain the requiredpressure differential and resulting braking effort. If for any reasonthe pressure should be built up in inlet chamber 80 beyond a desiredpressure level, the pressure relief valve 152 will open, connecting theinlet chamber with outlet chamber through passages not shown so as toestablish the pressure limit. 1

Upon brake release, the input .member 70 is moved rearwardly by spring140, slightly opening the valve faces and permitting a decrease in thepressure differential across power piston 78. When the brake is fullyreleased, the valve 132 returns to its at-rest position with the valvereturn bumper 138 having cushioned its engagement withthe cylinder rearwall 46. As the reaction piston 110 moves forwardly relative to powerpiston 78 upon brake release, it is similarly cushioned by snubber 116.

When the vehicle in which the booster is installed is operated duringvery cold weather, the booster must allow for the pressure influence ofthe cold viscous oil being pumped through the valve without applying thebrakes and causing a dragging brake operation even though the vehicleoperator has not applied the brakes. This is accomplished by allowingthe power piston 78 to move slightly under the pressure influence of thecold viscous oil without pulling the valve 132 with the piston. Thisslight piston travel results in an increased valve opening before thepiston travel is sufficient to apply the brakes through the mastercylinder. This amount of piston travel is most easily provided for byestablishing the length of push rod 58 so that the rear end of the pushrod is slightly disengaged from the power piston when the booster is inthe condition shown in FIG. 2. This is easily accomplished since theforward position of push rod 58 is determined by the master cylinderstop acting to position the master cylinder piston. This positioning ofthe master cylinder piston against a stop is well known in the mastercylinderart.

The separating valve arrangement also minimizes the piston travelnecessary to actuate the booster unit since the at-rest valve openingcan be set for warm hydraulic fluid operating conditions which usuallyexist after the pump has been pumping the fluid through the system for atime. The action of the separating valve described above is alsoadvantageous when foreign material is entrained in the hydraulic system.If, for example, a piece of rubber-like material or a small metalparticle becomes so entrained, the foreign element will lodge in thevalve opening, producing a reaction similar to that of the cold viscousoil, causing a slight buildup in pressure which moves the power pistonto open the valve to a greater extent. This will allow the foreignobject to pass through the valve easily and not affect brake boostercontrol. v

The noise .level of the booster assembly relates, among otherfactors, tothe natural frequency of vibration of various booster components and thecyclic pressure pulses generated by valveoperation. When thesefrequencies and pulses are sympathetic, noise at an objectionable levelmay be generated. It has been found, in units suitable in size forpassenger car use, that an angle 0 of 30 reduces the noise to anacceptable level. In heavier units, suitable for trucks, for example,the angle 0 may be as much as 45. In some instances with such heavierunits the tapered outlet and inlet angles a and b may be omitted and thevalve face angle may be the same as the valve seat angle. This ispermitted when the natural frequencies of vibration of components aresubstantially different from the cyclic pulses, and a short valve seatface is used. When cavitationgenerated noises are at objectionablelevels, the dual valve face arrangement,.giving aventuri effect,contributes to noise reduction.

What is claimed is:

l. A hydraulic brake booster comprising:

a housing;

a power piston reciprocably received in said housing and'definingtherewith an inlet chamber operatively fluid connected to a source ofhydraulic fluid pressure and an outlet chamber on the other side of saidpiston from said inlet chamber;

said piston having a stepped recess therein opening on the inlet chamberside thereof and a passage therethrough fluid connecting said recess andsaid outlet chamber; an input member extending into said inlet chamberand connected to be actuated by a brake pedal;

an output member engageable with said power piston to transmit forcebetween said power piston and a master cylinder and extending out ofsaid outlet chamber; and open center control valve means including aradially floating first valve element received in said piston recess andan axially movable second valve element on said input member, said valveelements having mating frusto-conical valve faces for controlling fluidflow between said inlet and outlet chambers,

an annular retainer circumferentially engaging said piston in axiallylocked relation and axially engaging said first valve element in axialforce exerting relation and retaining said first valve elementagainstaxial movement relative to said piston while resistably pemiittingradial floating movement of said first valve element in said pistonrecess, yieldable means urging said second valve element axially awayfrom said first valve element and in position against a stop pro- 10

1. A hydraulic brake booster comprising: a housing; a power piston reciprocably received in said housing and defining therewith an inlet chamber operatively fluid connected to a source of hydraulic fluid pressure and an outlet chamber on the other side of said piston from said inlet chamber; said piston having a stepped recess therein opening on the inlet chamber side thereof and a passage therethrough fluid connecting said recess and said outlet chamber; an input member extending into said inlet chamber and connected to be actuated by a brake pedal; an output member engageable with said power piston to transmit force between said power piston and a master cylinder and extending out of said outlet chamber; and open center control valve means including a radially floating first valve element received in said piston recess and an axially movable second valve element on said input member, said valve elements having mating frusto-conical valve faces for controlling fluid flow between said inlet and outlet chambers, an annular retainer circumferentially engaging said piston in axially locked relation and axially engaging said first valve element in axial force exerting relation and retaining said first valve element against axial movement relative to said piston while resistably permitting radial floating movement of said first valve element in said piston recess, yieldable means urging said second valve element axially away from said first valve element and in position against a stop provided on said housing, and reaction means subject to a force indicative of the booster output and transmitting said force to said input member; said valve elements being initially engageable in mating relation upon brake actuation to center said first valve element relative to said second valve element to establish and maintain a concentric annular orifice between said faces. 